I don't see anything wrong with 2 heat sources, however if you have the option of a space heater for the room you could also use that.
I use the ProProducts heat panels and love them. I have 4 and I don't have any other heat sources in the cages. I do run a space heater in the room.
My 7 foot boa is in a 4' wide by 30" deep and 20" tall. I like a bit of ceiling space and I wish I would have gone with a 2 foot tall unit.
Boas will display semi arboreal behaviors if you set them up for it.
The boa cage is on the bottom. This is an older photo but you can see the hides, the perches (3) and the water bowl.
https://i.imgur.com/1ydHH0M.jpg
Here is a more recent photo.
https://i.imgur.com/VyMdd9N.jpg
The boa cage is on the bottom, the carpet cage is in the middle and the royal python is on the top.
You can see the placement of the heat panel in the top cage in both pictures above.
In a 6 foot cage, the heat panel will be fairly large. My panel is placed in the center of the left half of the cage (visible in the upper left here). This cage is 6' x 30" x 24".
I have no issues with heat.
https://i.imgur.com/MshdZYr.jpg
Perches are all heavy duty for a SD x dwarf retic. This snake is more arboreal than both the boa and carpet python.
I use cypress, Reptile bark and coco husk in every cage.
I hope you enjoy setting up your future cage. It is pretty rewarding and relaxing to walk into a snake room and see this.
https://i.imgur.com/TNIRdbM.jpg
Good luck!